In conventional nonvolatile semiconductor memory devices of a floating gate electrode type, with the miniaturization of memory cells, the number of electrons accumulated in a floating gate electrode reduces. Accordingly, the leak of one electron among electrons accumulated in the floating gate electrode causes a large variation of the threshold value of a memory cell transistor, which is a factor of the deterioration of operation reliability. Moreover, the decrease in the interval between adjacent memory cells increases the interference due to capacity coupling, which causes the increase in a program time and an erase time and is a factor of the deterioration of the device characteristics.